Large numbers of smart devices are permeating our environment to collect data and act on the insight derived. Examples of such devices include smart homes, factories, cars, or wearables. For privacy, security, and safety, ensuring correctness of the configuration of these devices is essential. One key mechanism to protect the software integrity of these devices is attestation. In this paper, we analyze the requirements for efficient attestation of large numbers of interconnected embedded systems. We present the first collective attestation protocol which allows attesting an unlimited number of devices. Simulation results show a run-time of 5:3 seconds in networks of 50; 000 low-end embedded devices.